MUCH of the “stimulus” bill is devoted to a backdoor undoing of one of Washington’s greatest achievements of recent years – welfare reform.

One of the most important changes of the Clinton-era reform law was replacing the individual entitlement to welfare with a block grant to the states. In the old system, the more people a state signed up for welfare, the more money it got from Washington. The block grant broke this link, creating an incentive for states to help people become self-supporting.

But, as The Post’s Charles Hurt has reported, slipped into the stimulus bill is a provision establishing a new $3 billion emergency fund to help states pay for added welfare recipients, with the federal government footing 80 percent of the cost for the new “clients.”

Plus, the bill would reward states for increasing caseloads, even if the growth came because the state had loosened its requirements for recipients to work.

This is radical change. States that succeed in getting people off welfare would lose the opportunity for increased federal funding. And states that make it easier to stay on welfare (by, say, raising the time limit from two years to five) would get rewarded with more taxpayer cash. The bill would even let states with rising welfare rolls still collect their “case-load reduction” bonuses.

In short, the measure will erode all the barriers to long-term welfare dependency that were at the heart of the 1996 reform.

And this is just for “cash assistance” welfare, or TANF (Temporary Assistance for Needy Families). Yet the bill also dramatically expands other forms of welfare.

For example, it would spend $87 billion to subsidize state Medicaid costs. As a result, still more of the middle-class would be shifted on to welfare.

It also boosts spending on food stamps by 12 percent to $16.5 billion; hikes funds for the federal school lunch program by $150 million; adds $500 million to the Women, Infants & Children nutrition program, and even throws in $50 million for the surplus-commodity (free government cheese) program.

And it gives income tax “cuts” to people who don’t pay income taxes – payments that are, in fact, simply another form of welfare.

By some estimates, the stimulus bill contains roughly $250 billion in welfare spending, another $6,700 for every poor man woman and child in this country, along with the erosion of the 1996 reforms. It can be counted on to “stimulate” the loss of another generation to welfare dependency.

Since Lyndon Johnson declared a “war on poverty” in 1965, this country has spent nearly $10 trillion on that cause. Yet, 44 years later, the poverty rate remains perilously close to where it was. By now we should have learned that throwing money at the problem doesn’t work.

As a state senator, Barack Obama opposed the 1996 welfare reform. As a candidate for president, he praised its results. Where does he stand now? Does he really want to return to welfare as we knew it before 1996 and put millions more Americans on the public dole?

Michael Tanner is a senior fellow at the Cato Institute (cato.org) and the author of “The Poverty of Welfare: Helping Others in Civil Society” and other books.